Not necessarily a big mistake. Maybe a room that’s smaller than expected, a garage that doesn’t fit everything, an outlet in the wrong place, or something you spent extra money on and barely use.
I’m interested in the decisions that seemed perfectly reasonable on paper but turned out differently once you actually lived in the house.
What would you do differently?

One thing I’m curious about is what happens to the original budget once construction actually starts.
You get an initial quote, but then come the change orders, allowance adjustments, upgrades, and unexpected invoices.

How do you keep track of what was originally included versus what you’re being charged now?

Are you using a spreadsheet, email, your builder’s software, or something else?

And looking back, what would you have done differently?

A lot of custom home discussions start with estimates, but it’s much harder to find what people actually ended up paying.
If you’ve completed a build (or you’re close), share whatever numbers you’re comfortable with:

State / region

Square footage

Original budget

Final cost or current projected total

Biggest unexpected expense

One thing you’d budget differently next time

Land included or excluded? Either is fine — just mention which.

Even approximate numbers are useful. No need to share your builder’s name or any personal details.

It would be interesting to see how different the original estimates were from the final bills.

One thing worth checking before signing a custom home contract: the allowances.
A builder can give you a quote that fits your budget while leaving surprisingly little room for the finishes you actually want.
Here’s a hypothetical example of how allowances can add up:

Kitchen cabinets
Builder allowance: $15,000 → Actual cost: $24,000 (+$9,000)
Countertops
Builder allowance: $5,000 → Actual cost: $8,000 (+$3,000)
Flooring
Builder allowance: $12,000 → Actual cost: $18,000 (+$6,000)
Lighting
Builder allowance: $3,000 → Actual cost: $6,000 (+$3,000)
Plumbing fixtures
Builder allowance: $5,000 → Actual cost: $9,000 (+$4,000)
Tile
Builder allowance: $5,000 → Actual cost: $10,000 (+$5,000)
TOTAL
Builder allowances: $45,000
Actual selections: $75,000

That’s $30,000 over the allowances without changing the floor plan or adding square footage. Depending on the contract, additional markup or labor charges could increase that difference.
Before signing, I’d want answers to these questions:

Does each allowance include materials, labor, installation, taxes, and delivery — or materials only?

Can you actually buy the finishes you want at those allowance amounts?

What markup applies when you exceed an allowance?

Can savings in one category offset overruns in another?

When do you need to finalize selections, and what happens if prices change?

The easiest way to catch this early is to price out your actual selections before signing, not after construction begins.

For anyone who’s built a custom home: which allowance turned out to be the most unrealistic?
Kitchen? Flooring? Electrical? Something else entirely?

I’ve been reading through discussions about custom home building, and one thing keeps coming up: the original budget and what people actually end up paying seem to be two very different numbers.
Which makes me wonder — does anyone actually finish close to the original estimate? :)
I’m not talking about someone deciding halfway through that they want a $40k kitchen upgrade. That’s a choice.
I’m more curious about the costs nobody really warned you about. Things that weren’t obvious in the contract, allowances that turned out to be unrealistic, or expenses that just appeared along the way.
If you’ve built a custom home, how far off was your original budget?
And looking back, was there something you could’ve caught earlier, or is this just how custom home building works?